Is that arty turret looking behind itself? How? When I was testing it I could only move it a little left or right.
No, the screenshot shows that the artillery cannon collides with the chassis. Which I'm pretty sure it didn't before.
Oh it's intentional, since 2.9.0. Basically, I gave arty tanks more depression(-15 => -12) and yes I did notice that about NF arty. So I reverted 0.5 degree(-12 => -12.5). If you view that "tank" thingy as a non-metal thingy, it's acceptable.